ID Iberian Chiffchaff on call

Mystery chiffchaff at Castricum 

Why this green-and-yellow bird is not an Iberian Chiffchaff 

Genetic identity of grey chiffchaffs in the Netherlands (with Peter de Knijff) About birds with Siberian Chiffchaff mtDNA (DB article)

Proven tristis (with Peter de Knijff)
Photographs of birds with Siberian Chiffchaffs mtDNA: make up your own mind instead of letting us tell you what to think!

Unexpected Siberian Chiffchaff look-alikes (with Peter de Knijff) Proven (nominate) Common Chiffchaffs can look scarily similar to Siberian 

Siberian Chiffchaff with Common Chiffchaff calls An mtDNA tristis with recorded Common Chiffchaffs calls


Chiffchaffs from the southeast
There's a new DNA proven vagrant to NW Europe: Chiffchaff ssp. brevirostris or caucasicus. Can they be ID'd in the field?